Flashlights of this type are already known from the prior art. A lamp is described, for example, in DE 29 50 850 [U.S. Pat. No. 4,307,439] that emits an essentially parallel light beam when the filament is at the focal point of the paraboloid of the reflector. The beam can be altered by displacing the bulb and the battery casing axially relative to the lamp head and the reflector. Such an axial displacement can be effected by moving the cylinder sleeve axially relative to the battery casing. This axial movement can be effected either by a simple axial sliding movement or by a turning movement, together with a screwthread or with an inclined-slot guide system, wherein an inclined slot is, for example, provided in the lamp head, and a pin that is arranged on the battery casing engages in the slot.
However, it is a disadvantage of such a flashlight that it is intended for the adjustment of the relative position between the lamp head and the light source to be as smooth as possible, but this has the consequence that the relative position between the lamp head or the reflector and the light source can be displaced involuntarily when the flashlight is just shaken slightly, shifting the focusing that has been set. This problem is a commonly observed one in the case of bicycle lamps in particular, which are subject to permanent shaking when in use.